Technical Field
The present disclosure relates to a process for producing a finely divided metal-doped aluminogallate nanocomposite and a method of NO decomposition using the nanocomposite.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
One of the limitations to the direct decomposition of nitrogen oxides is the lack of robust catalysts capable of performing under real world conditions. Nitrogen oxides (NOx=NO+NO2) are a well-known class of toxic byproducts from the combustion of hydrocarbon fuels [see, Nirisen et al., US2004/0023796A1, incorporated herein by reference in its entirety]. An increasing number of environmental and health issues including elevated ozone production, acid rain fall, soil contamination and cyanosis in humans are linked to increased NOx production.
A potential solution for combating NOx production is the catalytically driven direct decomposition reaction which converts NOx into N2 and O2. The reaction which can take place with or without a reducing agent requires a catalyst to be stable under “real world” conditions including the presence of sulfates (SO2), H2O vapor, prolonged catalytic use and reaction temperatures in excess of 300° C. However, decomposition without the presence of a reducing agent proceeds considerably slower than reactions with the reducing agent [See Luo, Y. M., 2004, “Influence of preparation methods on selective catalytic reduction of nitric oxides by propene over silver-alumina catalyst,” Catalysis Today incorporated herein by reference in its entirety]. This makes reaction mechanisms with a reducing agent (such as a hydrocarbon) the preferred decomposition route for NOx. These conditions are consistent with applications such as those required within an automotive catalytic converter.
Some existing methods for making catalytic materials with NOx decomposition potential include sol-gel, co-precipitation and hydrothermal processes [See Pitukmanorom, P., 2009, “Selective catalytic reduction of nitric oxide by propene over In2O3/Al2O3 nanocomposites,” Nano Today incorporated herein by reference in its entirety]. Single metal oxides, multiple metal composite oxides, zeolites doped with transition metals, and three-way catalysts (TWCs) made from the above processes have been investigated [See Matsumoto, S., 2004, “Recent Advances in automobile exhaust catalysts,” Catalysis Today incorporated herein by reference in its entirety]. For example, γ phase Al2O3, and γ-Ga2O3—Al2O3 made from co-precipitation and hydrothermal processes respectively in the presence of a reducing agent have effectively catalyzed NO decomposition, while transition metal-doped γ-Al2O3 show improved stability in the presence of H2O vapor and SO2 [See Pitukmanorom, P., 2009, “Selective catalytic reduction of nitric oxide by propene over In2O3/Al2O3 nanocomposites,” Nano Today incorporated herein by reference in its entirety].
Unfortunately, the catalytic activities of these materials were either extinguished in the presence of H2O vapor, SO2, or require reaction conditions that are not consistent with any real world applications [See Sloczynski, J., 1999, “Oxidative Dehydrogenation of propane on NixMg1-x Al2O4 and NiCr2O4 Spinels” Journal of Catalysis incorporated herein by reference in its entirety]. Additionally, γ-Ga2O3—Al2O3 and transition metal-doped γ-Al2O3 undergo heat induced phase transitions at elevated reaction temperatures which limit catalytic activity. Meanwhile, calcinating and/or milling steps (which are commonly used in co-precipitation and sol-gel processes to make solid solution products) promote unrestricted grain growth giving rise to γ-Ga2O3—Al2O3 and transition metal-doped γ-Al2O3 materials with variable nanoparticle diameters [See Aguilar-Rios, G., 1995, “Hydrogen interactions and catalytic properties of platinum-tinsupported on zinc aluminate,” Applied Catalysis A incorporated herein by reference in its entirety]. These variably sized nanoparticles provide low yielding reaction surface areas which limit NO), decomposition efficiencies.
In view of the foregoing, one object of the present disclosure is to present a process for making a robust NOx decomposition catalyst and a method of using said catalyst.